Operation Plumbbob

Operation Plumbbob was a series of nuclear tests conducted between May 28 and October 7, 1957 at the Nevada Test Site, following Operation Redwing, and preceding Operation Hardtack I. It was the biggest, longest, and most controversial test series in the continental United States.

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Background

The operation was the sixth test series and consisted of 29 explosions, of which two did not produce any nuclear yield. 21 laboratories and government agencies were involved. While most Operation Plumbbob tests contributed to the development of warheads for intercontinental and intermediate range missiles, they also tested air defense and anti-submarine warheads with small yields. They included 43 military effects tests on civil and military structures, radiation and bio-medical studies, and aircraft structural tests. Operation Plumbbob had the tallest tower tests to date in the U.S. nuclear testing program, as well as high-altitude balloon tests. One nuclear test involved the largest troop maneuver ever associated with U.S. nuclear testing.

Approximately 18,000 members of the U.S. Air Force, Army, Navy and Marines participated in exercises Desert Rock VII and VIII during Operation Plumbbob. The military was interested in knowing how the average foot-soldier would stand up, physically and psychologically, to the rigors of the tactical nuclear battlefield.

Studies were conducted of radiation contamination and fallout from a simulated accidental detonation of a weapon; and projects concerning earth motion, blast loading and neutron output were carried out.

Nuclear weapons safety experiments were conducted to study the possibility of a nuclear weapon detonation during an accident. On July 26 1957, a safety experiment, "Pascal-A" was detonated in an unstemmed hole at NTS, becoming the first underground shaft nuclear test. The knowledge gained here would provide data to prevent nuclear yields in case of accidential detonations, for example a plane crash.

The Rainier shot, conducted September 19 1957, was the first fully contained underground nuclear test, meaning that no fission products were vented into the atmosphere. This test of 1.7 kilotons could be detected around the world by seismologists using ordinary seismic instruments. The Rainier test became the prototype for larger and more powerful underground tests.

Radiological effects

Plumbbob released 58,300 kilocuries (2.16 EBq) of radioiodine (I-131) into the atmosphere. This produced total civilian radiation exposures amounting to 120 million person-rads of thyroid tissue exposure (about 32% of all exposure due to continental nuclear tests). Statistically speaking, this level of exposure would be expected to eventually cause about 38,000 cases of thyroid cancer, leading to some 1,900 deaths^{[citation needed]}. No hard data is available on the long-term civilian effects of these tests.

In addition to civilian exposure, troop exercises conducted near the ground near shot "Smoky" exposed over three thousand servicemen to relatively high levels of radiation. A survey of these servicemen in 1980 found significantly elevated rates of leukemia: ten cases, instead of the baseline expected four.

List of tests

The tests comprising Operation Plumbbob were as follows in TNT equivalent:

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According to urban legend, a manhole cover was accidentally launched from its shaft during an underground nuclear test in the 1950s, at great enough speed to achieve escape velocity. The myth is based on a real incident during the Pascal-B nuclear test, where a heavy (900 kg) steel plate cap was blasted off the test shaft at an unknown velocity, and appears as a blur on a single frame of film of the test, and was never recovered. A calculation before the event gave a predicted speed of 6 times Earth escape velocity, but the calculation is unlikely to have been accurate and they did not believe that it would leave the Earth in reality. After the event, Dr. Robert R. Brownlee described the best estimate of the cover's speed from the photographic evidence as "going like a bat!!"^[1]

This incident was used as part of the technical justification for the Orion project.

References

• Department of Energy of Nevada Original source for test information.
• Plumbbob page on the Nuclear Weapons Archive (also refers to manhole cover issue mentioned above).
• National Cancer Institute Study Estimating Thyroid Doses of I-131 Received by Americans From Nevada Atmospheric Nuclear Bomb Test, 1997

Notes

1. ^ Learning to Contain Underground Nuclear Explosions By Dr. Robert R. Brownlee - June 2002